Precision Time Measurement (PTM) is a PCI Express 3.0 feature that measures the time over the PCIe bus and provides synchronization messages to alert host programs about changes in the time it takes for data to travel across to PCIe bus. This feature is especially useful since data transfers between device and host are not symmetric in terms of time taken for transfer from host to device versus device to host.
When first trying to understand whether a system supports PTM or not, I had a look at the Open Compute Platform page related to this feature. However, I found inaccuracies in the page and was not confident in the completeness of the page’s information.
The page lists that the following CPUs are supported.
- Intel Core, Gen 11 (Rocket Lake)
- Intel Core, Gen 12 (Alder Lake)
- Intel Core, Gen 13 (Raptor Lake)
This listing is inaccurate though in that Intel Gen 11 is Tiger Lake, Intel Gen 12 is Alder Lake, and Intel Gen 13 and 14 are Raptor Lake.
My laptop has a Tiger Lake processor, so I was unsure whether or not it would actually support PTM. Luckily PTM is an extended PCI capability, so whether it is supported or not can be checked by querying the capabilities of the PCI bridge associated with my host CPU by using pci sysfs nodes. The program uses pciutils to wrap the work of these sysfs node queries.
I was able to determine that my laptop did indeed support PTM using this tool.
sudo ./ptmcheck
0000:00:01.1 vendor=8086 device=9a05 class=0604 irq=0 (pin 2) base0=0 (Device 9a05)
0000:00:01.0 vendor=8086 device=9a01 class=0604 irq=0 (pin 1) base0=0 (11th Gen Core Processor PCIe Controller #1)
0000:00:1c.0 vendor=8086 device=43be class=0604 irq=0 (pin 3) base0=0 (Device 43be)
The above bridge devices reported having the PTM PCI capability
Host system appears to support Precision Time MeasurementThe tool only checks the capabilities of bridges to avoid conflating PCI device support with host support for PTM.
sudo lspci -s 0000:00:01 -v
00:01.0 PCI bridge: Intel Corporation 11th Gen Core Processor PCIe Controller #1 (rev 05) (prog-if 00 [Normal decode])
Subsystem: Dell Device 0a5e
Flags: bus master, fast devsel, latency 0, IRQ 126
Bus: primary=00, secondary=01, subordinate=01, sec-latency=0
I/O behind bridge: 3000-3fff [size=4K] [16-bit]
Memory behind bridge: a9000000-aa0fffff [size=17M] [32-bit]
Prefetchable memory behind bridge: 6000000000-6201ffffff [size=8224M] [32-bit]
Capabilities: [40] Express Root Port (Slot+), MSI 00
Capabilities: [80] MSI: Enable+ Count=1/1 Maskable- 64bit-
Capabilities: [90] Subsystem: Dell Device 0a5e
Capabilities: [a0] Power Management version 3
Capabilities: [100] Advanced Error Reporting
Capabilities: [220] Access Control Services
Capabilities: [200] L1 PM Substates
Capabilities: [150] Precision Time Measurement
Capabilities: [280] Virtual Channel
Capabilities: [a00] Downstream Port Containment
Capabilities: [a30] Secondary PCI Express
Capabilities: [a90] Data Link Feature <?>
Capabilities: [a9c] Physical Layer 16.0 GT/s <?>
Capabilities: [edc] Lane Margining at the Receiver <?>
Kernel driver in use: pcieport
00:01.1 PCI bridge: Intel Corporation Device 9a05 (rev 05) (prog-if 00 [Normal decode])
Subsystem: Dell Device 0a5e
Flags: bus master, fast devsel, latency 0, IRQ 127
Bus: primary=00, secondary=02, subordinate=02, sec-latency=0
I/O behind bridge: [disabled] [16-bit]
Memory behind bridge: aa200000-aa2fffff [size=1M] [32-bit]
Prefetchable memory behind bridge: [disabled] [64-bit]
Capabilities: [40] Express Root Port (Slot+), MSI 00
Capabilities: [80] MSI: Enable+ Count=1/1 Maskable- 64bit-
Capabilities: [90] Subsystem: Dell Device 0a5e
Capabilities: [a0] Power Management version 3
Capabilities: [100] Advanced Error Reporting
Capabilities: [220] Access Control Services
Capabilities: [200] L1 PM Substates
Capabilities: [150] Precision Time Measurement
Capabilities: [280] Virtual Channel
Capabilities: [a00] Downstream Port Containment
Capabilities: [a30] Secondary PCI Express
Capabilities: [a90] Data Link Feature <?>
Capabilities: [a9c] Physical Layer 16.0 GT/s <?>
Capabilities: [edc] Lane Margining at the Receiver <?>
Kernel driver in use: pcieport
sudo lspci -s 0000:00:1c -v
00:1c.0 PCI bridge: Intel Corporation Device 43be (rev 11) (prog-if 00 [Normal decode])
Subsystem: Dell Device 0a5e
Flags: bus master, fast devsel, latency 0, IRQ 132
Bus: primary=00, secondary=ab, subordinate=ab, sec-latency=0
I/O behind bridge: [disabled] [16-bit]
Memory behind bridge: aa100000-aa1fffff [size=1M] [32-bit]
Prefetchable memory behind bridge: [disabled] [64-bit]
Capabilities: [40] Express Root Port (Slot+), MSI 00
Capabilities: [80] MSI: Enable+ Count=1/1 Maskable- 64bit-
Capabilities: [90] Subsystem: Dell Device 0a5e
Capabilities: [a0] Power Management version 3
Capabilities: [100] Advanced Error Reporting
Capabilities: [220] Access Control Services
Capabilities: [150] Precision Time Measurement
Capabilities: [200] L1 PM Substates
Capabilities: [a30] Secondary PCI Express
Capabilities: [a00] Downstream Port Containment
Kernel driver in use: pcieportThe only prerequisites for building ptmcheck are pciutils, a C toolchain
(defaults to gcc but can be overridden using CC), and GNU make.
To generate the ptmcheck binary, simply run make. Use make clean to clean
up build artifacts in the project directory.
ptmcheck takes no arguments and requires elevated privileges (which it checks for).
An example of ptmcheck when used without elevated privileges.
./ptmcheck
Need to run program with elevated privileges!An example of ptmcheck output when run on a system without PTM support.
sudo ./ptmcheck
Host system has no bridges that reported the PTM PCI capabilityAn example of ptmcheck output when run on a system with PTM support.
sudo ./ptmcheck
0000:00:01.1 vendor=8086 device=9a05 class=0604 irq=0 (pin 2) base0=0 (Device 9a05)
0000:00:01.0 vendor=8086 device=9a01 class=0604 irq=0 (pin 1) base0=0 (11th Gen Core Processor PCIe Controller #1)
0000:00:1c.0 vendor=8086 device=43be class=0604 irq=0 (pin 3) base0=0 (Device 43be)
The above bridge devices reported having the PTM PCI capability
Host system appears to support Precision Time Measurement